This disclosure relates to a computer-assisted process for the design and placement of multi-colored patterns on absorbent substrates using a limited number of transparent process colorants. Specifically, this disclosure relates to a process by which a designer, working with a computer-aided design system, can generate and accurately represent on a computer monitor or similar display a multi-colored pattern, as that pattern would appear on a specified absorbent substrate, using coloring elements comprised of groups of multiple pixels in which process colorants have been mixed in a controlled manner to expand the range of available colors, and to compensate for colorant delivery limitations that prevent the application of small, accurately metered quantities of colorant. In an embodiment incorporating the process disclosed herein, specific actuation instructions for a specific dye injection machine capable of patterning a moving textile substrate may be generated.
Of the various methods that may be used to apply a pattern of colorants (e.g., dyes) to a textile web, arguably the most versatile method involves the pixel-wise application of measured quantities of liquid colorants, under the control of a computer containing a patterning program, to form multi-colored patterns using a predetermined set of primary or process colors. Examples of such pattern generation techniques may be found in commonly assigned U.S. Pat. Nos. 4,033,154; 4,116,626; 4,545,086; 4,984,169, and 5,195,043, hereby incorporated by reference herein.
Although the teachings herein are not limited to such machines, the machines embodying the patterning techniques described in the above-listed patent documents are particularly well-adapted for patterning webs of textile substrates. Such machines are characterized by a series of fixed, linear arrays or xe2x80x9ccolor barsxe2x80x9d comprised of a plurality of individually controllable liquid colorant applicators or jets, each array being supplied by a respective liquid colorant supply system carrying liquid colorant (a xe2x80x9cprocess colorantxe2x80x9d) of a specified color (known as a xe2x80x9cprocessxe2x80x9d color). The arrays are positioned in parallel relationship, spanning the width of the path taken by the substrate to be patterned, and the arrays are generally perpendicular to the direction of web travel.
As the substrate moves along its path, it passes under each of the arrays in turn and receives, at predetermined locations on the substrate surface (i.e., at the pixel locations specified by the pattern data), a carefully metered quantity of dye from one or more of the dye jets spaced along the array or color bar. The control system associated with the machine provides for the capability of delivering a precise quantity of dye or other liquid colorant (which quantity may be varied in accordance with the desired pattern) at each specified location on the substrate as the substrate moves under each respective array, in accordance with electronically defined pattern information.
Because the jets on each array are capable only of dispensing the liquid dye supplied to that array, the maximum number of different colors that can be directly applied to the substrate by the machine (i.e., the maximum number of process colors) in a given pass can be no greater than the number of arrays. Additionally, due to the physical limitations associated with the individual liquid dye applicators, there is some non-zero minimum quantity of colorant that can be accurately and repeatedly metered onto the substrate, typically representing the limit as to how quickly the valves controlling colorant delivery can be made to turn on and off. This becomes an important issue when the pattern color to be reproduced requires a combination of process colors having a relatively low proportion of a certain colorant (e.g., xe2x80x9cColorant Axe2x80x9d), and the patterning system cannot deliver Colorant A to that specific pattern location except in an amount that significantly exceeds the quantity needed. These two conditionsxe2x80x94a limited number of process colorants and a minimum colorant delivery systemxe2x80x94represent limitations to the range of colors that can be represented on the substrate. Unless specifically stated otherwise, the terms xe2x80x9cdyexe2x80x9d and xe2x80x9ccolorantxe2x80x9d shall be used interchangeably herein to indicate a liquid colorant that is intended to include, but is not necessarily limited to, textile dyes.
A recurring challenge associated with such devices having a limited number of process colorants is devising ways to allow for the reproduction of the widest possible range of colors (i.e., reproducing the maximum number of different target colors) from a given set of conditions, i.e., the given set of process colorants and the minimum colorant delivery limitation. Among the techniques used in the graphics arts industry to extend the range of reproduced colors from a limited number of process colors (which, in the patterning devices discussed above, correspond to the number of arrays or color bars) are two techniques that shall be referred to herein as (1) dithering and halftoning techniques and (2) in situ bending techniques.
Briefly, dithering and halftoning techniques involve the use of pixels (pattern elements), usually of varying colors, that are arranged in checkerboard-like patterns to simulate, when viewed at a distance, the appearance of colors that are not represented by process colorants. For example, various shades of gray may be constructed by a checkerboard of small black and white print dots of different relative sizes. Where necessary for clarity, this discussion will distinguish dithering techniques, which are sometimes associated only with pattern areas in which the color is non-uniform, from halftone techniques, useful in pattern areas in which a continuous or uniform color is desired. In the latter, a group of pixels (i.e., a superpixel) that collectively expresses the proper color is tiled, as a repeating unit, into the appropriate pattern areas. In situ blending techniques, as used herein, involve the physical mixing of colorants within individual pixels or groups of pixels (i.e., superpixels) to generate colors that are not represented by process colorants.
Traditional dithering and halftoning techniques are based upon the phenomenon that a target color for which no exact match is available among the process colors can be visually approximated, often to a high degree of accuracy, by the juxtaposition of several individual pixels, each having a color that expresses a visual component of the desired or target color. When viewed at an appropriate distance, the eye tends to visually integrate or blend the individual contribution of each pixel in this group of adjacent pixels and provides the perception of the target color that, in reality, has been xe2x80x9cconstructedxe2x80x9d from a mosaic of individual component colors (additive color mixing). However, note that even in traditional printing systems new colors are produced when print dots overlap. In addition, as further elaborated below, colorants in neighboring pixels mix together in some print systems. In the latter case, the individual pixels create a new color (subtractive color mixing) that can be spatially uniform.
An in situ blend shall refer to the color of the physical combination of two or more colorants that occupy at least portions of the same pixel-sized location on a substrate, as viewed at the individual pixel level. The additional colorants might have been applied to that pixel by the patterning device, or the additional colorant(s) might have migrated from an adjacent pixel. Accordingly, if the color green is to be reproduced in a given area and only yellow and blue colorants are available as process colors, the designer may (providing the patterning device is capable) elect to deliver, in a specified sequence, a predetermined quantity of yellow and a predetermined (and not necessarily equal) quantity of blue to each pixel in that area, to form the desired color green in each of the pixels comprising that area, rather than constructing the green using halftone (xe2x80x9ccheckerboardingxe2x80x9d) methods.
Consistent with the above, as used herein the term xe2x80x9cpixelxe2x80x9d shall refer to the smallest area or location in a pattern or on a substrate that can be individually addressable or assignable with a given color. Alternatively, if clear from the context, the term xe2x80x9cpixelxe2x80x9d shall refer to the smallest pattern element necessary to define the line elements of the pattern to a predetermined level of detail, analogous to the pixel counts in imaging device resolution specifications (e.g., xe2x80x9c1280xc3x971024xe2x80x9d).
Both dithering/halftoning and in situ blending techniques are well suited to systems in which the reproduced patterns are comprised of small quantities of different colorants that are deposited in contiguous, pixel-wise fashion, across the surface of the substrate, whether or not the colorants are dispensed from fixed color bars. While both of these techniques may be employed separately, these two techniques can be combined to form a much wider range of reproducible colors that would be possible by using either technique alone.
The term xe2x80x9cperceived colorxe2x80x9d shall refer to the color of a small area of a substrate in which a target color has been reproduced using dithering techniques, wherein the colors of adjacent individual pixels are visually integrated by the eye of the observer to form a visual blend that is perceived as the target color.
The term xe2x80x9ctarget colorxe2x80x9d will refer to the desired observed color to be reproduced within the pattern on the substrate. The term xe2x80x9cprocess colorxe2x80x9d will refer to the inherent color of the individual, unblended dye or other colorant that may be directly applied in pixel-wise fashion to the substrate by the individual dye jet; comprising a given array. Note that the same process colorant may have a different visual appearance on different substrates, due to inherent substrate color, substrate texture, etc.
For purposes of the following discussion, an arrangement of xe2x80x9cNxe2x80x9d individual pixels of various colors (two, three, or more) in a checkerboard-like array to simulate color as the result of a dithering or halftoning process shall be referred to as a xe2x80x9cstructural blend.xe2x80x9d A xe2x80x9cpurexe2x80x9d structural blend shall be one in which no more that one process color has been applied to each pixel. For example, to generate the color green using only blue and yellow colorants in a pure structural blend, alternating xe2x80x9cchecksxe2x80x9d (i.e., pixels) of 100% blue and 100% yellow may be used to yield a localized pattern comprised of a 50%/50% blend of blue and yellow. Note that the total amount of colorant delivered to each pixel does not exceed 100%, the absorptive capacity of the substrate.
As mentioned above, where an extremely broad range of target colors must be created from a limited number of available or primary colors, it has been found advantageous to form dithered structures that are comprised of individual pixels in which in situ blending may have occurred. Such in situ blending may be the result of migration of colorants from one pixel containing a colorant to an adjoining pixel containing a different colorant (xe2x80x9cinter-pixel blendingxe2x80x9d), the direct application of two or more different colorants within the same pixel (xe2x80x9cintra-pixel blendingxe2x80x9d), or a combination of these two techniques, in which the inter-pixel colorant migration involves at least two pixels into which two or more individual colorants have been delivered by the patterning device. This provides for the possibility that, within a dithered structure, some pixels may carry the color of a process color, while others may carry a color that is the result of the physical blending of two or more of the process colors. Dithered structures in which at least some of the individual pixels comprising the checkerboard xe2x80x9cchecksxe2x80x9d are colored by the presence of two or more different process colorants in the same pixel shall be referred to as xe2x80x9chybridxe2x80x9d structural blends.
The term xe2x80x9csuperpixelxe2x80x9d shall be used to describe a group of xe2x80x9cNxe2x80x9d pixels, most commonly, a square array of pixels (e.g., 2xc3x972, 3xc3x973, 4xc3x974, etc.), that is created by an appropriate halftoning algorithm as a unit, i.e., the multi-pixel group is treated as a single large pixel, having, for dithering purposes, an assigned dithering palette color dictated by the color and arrangement of the individual pixels of which it is comprised. If, for example, medium blue and black colorants have been applied in alternating fashion to the constituent pixels of the superpixel, the superpixel will appear to have a dark blue color. This dark blue superpixel then may be used by an appropriate dithering algorithm in the same manner that an individual pixel, carrying a xe2x80x9cprocessxe2x80x9d color of dark blue, would be used.
Superpixels may be used once during dithering, or many times, as a repeating unit that is xe2x80x9ctiledxe2x80x9d or geometrically replicated over an area of the pattern that is required to carry a uniform color that cannot be reproduced using process colors and single-pixel color blending techniques (e.g., in-situ blending). For discussion purposes herein, it shall be assumed that the superpixel shall not be comprised of so many individual pixels N as to preclude the uniform migration of dye throughout the superpixel. Where this assumption is not valid, the resulting superpixels may tend to exhibit a noticeable degree of unevenness or non-uniformity of coloration, often referred to as xe2x80x9cheatherxe2x80x9d or xe2x80x9cgranularity,xe2x80x9d that may be aesthetically undesirable. In the practice of the instant method, N values of 9 and 16 have produced acceptable results, although it is known that, generally speaking, larger values of N tend to produce heather, stippling, or other pattern artifacts. The threshold value of N for which this condition holds will depend upon the nature of the substrate, the quantity and viscosity of the applied inks or dyes, the patterning technique used, etc. Conventionally, the total colorant concentration assigned to any individual pixel comprising a superpixel is limited to about 100% in order to discourage excessive colorant migration outside the pixel, as well as to avoid potential drying problems, etc. The term xe2x80x9cconcentrationxe2x80x9d is an expression of the percentage of total substrate volumetric absorption capacity taken up by the colorant, and is not an expression of the relative dilution or chromophore content of the liquid colorantxe2x80x94i.e., a colorant applied to a pixel at a 50% concentration means that the pixel has been saturated to one half the absorptive capacity of the substrate to absorb colorant at that location, and additional colorant(s) may be applied, up to a limit of 100% concentration, without exceeding the nominal absorptive capacity of the substrate at that location.
In cases where the absorptive capacity of the substrate is exceeded, further opportunities to expand the range of reproduced color become available. A superpixel in which the 100% maximum colorant absorptive capacity of some pixels are exceeded shall be referred to as a metapixel. Colors of a metapixel can depend heavily upon the controlled physical mixing or blending of colorants beyond the boundaries of certain individual pixels within the metapixel. To form a metapixel, liquid colorant is applied in unequal quantities to adjacent pixels, the objective being to selectively oversaturate certain pixels (i.e., achieve a colorant concentration greater than 100% within those pixels) and, at the same time, undersaturate other, adjacent pixels (i.e., restrict the colorant concentration to less than 100% within those pixels), so that the overall colorant concentration of the metapixel is maintained at a desirable level. The average concentration of colorant within any superpixel, including a metapixel, preferably is maintained at no more than 100% to avoid any of the undesirable effects of substrate oversaturation (e.g., difficulty in fixing or drying, uncontrolled migration of colorants, etc).
It should be understood that the color-forming techniques described herein are not limited to the specific patterning systems described above. For example, an arrangement of liquid colorant (e.g., dye) applicators, perhaps grouped in terms of color to be applied, may be physically moved or traversed across the path of a sequentially indexed substrate while selectively dispensing measured quantities of colorant onto the substrate at pre-defined locations. Although such arrangement is distinct from the fixed array systems discussed above, it is believed that the teachings herein are fully applicable to and adaptable for use with any such automated systems in which dye or colorant delivery can be controlled to the extent necessary to place reliably a pre-defined quantity of one or more liquid colorants at pre-specified locations on an absorbent substrate. Alternatively, it is contemplated that the techniques described herein could be applied to patterning systems using print screens with absorbent substrates. In all cases the substrate must be sufficiently absorbent to permit a superpixel size within which inter-pixel dye migration is essentially complete. For example, bond paper is generally not absorbent enough to qualify as a satisfactory substrate in this regard.
It also should be understood that the techniques described herein are applicable to the patterning of a variety of absorbent substrates, but will be described in terms of an absorbent substrate such as a textile substrate. Furthermore, while carpet substrates are specifically discussed herein, it should be understood that other textile substrates, such as decorative or upholstery fabrics, or other absorbent substrates, may also be used, with appropriate modifications to the processes discussed below that would naturally occur to one skilled in the art.
The above description is directed to the various ways to expand the range of reproducible colors that can be formed from a limited number of process colors, and to accommodate physical limitations in the delivery of small quantities of colorant to specific locations on the substrate. The following discussion will reveal how a designer can substantially automate the process of developing arrangements and blends of process colors, particularly through the use of superpixels, to successfully reproduce a wide range of target colors on a specific absorbent substrate and effectively overcome the obstacles associated with the limited range of process color availability and inadequate colorant delivery response times.
The processes disclosed herein provide a comprehensive capability whereby superpixel structures can be constructed automatically to render a wide range of designer-developed colors, and those colors can be accurately predicted and portrayed in pattern areas for designer review on a computer monitor. Additionally, such colors can be made a part of the dithering palette of an appropriate dithering program. Accordingly, the teachings herein provide the designer or artist with a substantially automated technique through which an existing set of process colors can be used to generate a significantly larger range of colors that would otherwise be available only through the highly labor-intensive process of manually constructing individual pixel structures.
To be of maximum benefit to the designer or artist, it is believed that any computer-based design system of the kind disclosed herein should address the following major requirements: (1) colors are specified by the designer only as relative concentrations of process colors; (2) colors must be accurately rendered on the design station display as they would appear on the substrate of interest; (3) colors must be convertible into superpixel structures that reproduce the color without manual intervention by the designer, i.e., the type of superpixelxe2x80x94solid shade, intra-pixel blended, xe2x80x9cpurexe2x80x9d structural, xe2x80x9chybridxe2x80x9d structural, or metapixelxe2x80x94and the portioning out of colorants to specific pixels must be fully automated; and, optionally, (4) the resulting superpixel structures should be translatable into patterning device instructions in a seamless manner, thereby extending the efficiency of the design process into the manufacturing process. This disclosure addresses each of these requirements, in the context of the overall pattern generation and reproduction process.
The color resulting from the application of a colorant to a substrate is influenced by the nature of the substrate. Accordingly, in order to predict with accuracy on a computer monitor the visual result of applying one or more colorantsxe2x80x94blended or unblendedxe2x80x94to an absorbent substrate, it is essential to account for certain physical properties of the substrate. In accordance with the teachings herein, Kubelka-Munk color blending theory is used. This theory utilizes the substrate""s light absorption and light scattering properties to calculate a reflectivity parameter for each colorant, which may then be used to predict the relative contribution of each component of a mixture of process colorants, and thereby predict (and represent on a computer monitor) the appearance of the colorants and colorant blends on the substrate. As extended in accordance with the teachings herein, Kubelka-Munk color blending theory has been found to be useful in determining the result of single or multiple dye applications (in any sequence) within a given pixel, and evaluating the effects of dye migration between the contiguous pixels that make up the superpixel.
A classic challenge associated with color blending is referred to as the xe2x80x9cinverse blendxe2x80x9d problem: while it is possible to calculate, using the techniques disclosed herein, the resulting color of a specified combination of colorants, applied in a given proportion and sequence, it is substantially more difficult to determine the colorant components and application sequence necessary to best reproduce a selected target color. While one set of blend concentrations will result in only one blend color (as defined by a color space, say, RGB values), the same blend color (again, defined by a color space, say, RGB values) generally may be produced by an infinite set of different blend concentrations. To overcome this problem, the innovative technique herein provides that, while process colors are specified in terms of RGB values for purposes of visual feedback, blends of process colors are specified by the designer in terms of concentrations (i.e., percent of total substrate absorptive capacity), rather than RGB values. By doing so, the problem of determining the best possible combination of dyes and proportions of dyes that will result in the desired color (expressed in RGB values)xe2x80x94the inverse blend problemxe2x80x94is eliminated.
As an additional advantage of this technique, the designer/artist is provided with the ability to adjust color by increasing the concentration of colorant, an intuitive process that is analogous to adjusting the quantity of each different xe2x80x9cpaintxe2x80x9d applied to a given area and that allows the designer/artist to better utilize his or her experience in conventional painting. Additionally, the teachings herein include a process which automates the construction of a superpixel having the desired target color. Mixtures of process colors are automatically constructed and then arranged within a superpixel structure so as to yield the desired overall color while minimizing patterning artifacts, and the results may be accurately portrayed on the design station monitor. While commercial systems like Adobe Photoshop(copyright) permit color specification through relative colorant concentrations (e.g., CMYK values), such systems generally are not applicable to printing on absorbent substrates due to a variety of technical considerations, including one or more of the following: the systems cannot take into account colorant stratification in the substrate when predicting colors for computer display, the systems do not provide for the formation of superpixels, the systems do not permit the use of arbitrary process colors, the systems cannot accommodate the use of metapixels, and the systems require that samples of all possible colors be printed and measured before accurate color display is possible.
Upon designer approval, the computer monitor image, as rendered by the graphics arts software, then may be translated into specifications or operating instructions for the patterning device. This process, when used with appropriately compatible automated hardware, is capable of providing for the automated manufacture of the patterned substrate, as that patterned substrate appeared on the designer""s monitor.